sedimentary

Chert (Yellow Jasper variant)

Microcrystalline Quartz (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Honey-yellow to ochre (caused by iron oxide inclusions); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Honey-yellow to ochre (caused by iron oxide inclusions)
Luster: Waxy to dull

Identified March 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from groundwaters in limestone or shale beds. Common in stratigraphic layers from the Paleozoic to Mesozoic eras.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal edges; currently used in jewelry (decorative cabochons), landscape gravel, and as a component in concrete.

Geological facts

Yellow chert/jasper was prized by Neolithic peoples for tool-making; it can create sparks when struck against steel, making it useful for fire-starting in survival situations.

Field identification & locations

Identify in the field by its smooth, waxy surface and shell-like (conchoidal) fracture lines. It is common in riverbeds and limestone outcrops globally. Tips for collectors: check for translucency at thin edges to distinguish from similar opaque rocks.

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Sandstone or Siltstone

Arenite (if sandstone)

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Sandstone

Arenite (primarily SiO2)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

Arenite (SiO2)

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Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

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